Such separators are well-known and generally use one or more taut screens of selected mesh size which are mounted in or on a chassis that is itself supported on a base by elastomeric mounts, springs or other resilient members. The chassis is coupled to a motor which drives offset weights to impart vibration to the chassis and thereby to the screen(s) of the sieve.
Separators are widely used in many industries and the use is determined by the materials to be sieved or separated, and these materials themselves determine the mesh size for the screen.
One industry in which such separators are widely used is the pharmaceutical industry. In this industry, it is of special importance that, when sieving a product, the probability of any sieved material escaping into the surrounding environment is restricted ideally to zero, but in reality to the lowest possible margin, so that neither workers nor other equipment nor products can become contaminated.
There are prior art arrangements to ensure that material fed to such a separator remains within its confines and one such separator is shown in FIG. 1 of the accompanying drawings.
FIG. 1 shows a typical separator 10 comprising a chassis 12 mounted on a rigid base frame 14. The separator has a motor driven out-of-balance weights vibrator 16 mounted on its side. The chassis 12 contains one or more mesh screens each stretched in a frame which is mounted securely over the hopper.
The separator also comprises a cover 18 (or lid) which is mounted on the chassis, and has an inlet 20 through which material to be separated can be loaded into the separator and has an observation port 21.
The cover 18 is fastened to the chassis in sealed engagement therewith by a plurality of toggle or over-centre clamps 22, the locking action of which secures the cover to the chassis. As good as the seals are that are established with such a structure, in practice, particles of sieved materials do escape from such separators and these particles, being of microfine dimensions can collect on surfaces of the separator and elsewhere, with the attendant possibility of contamination when the separator is used for separating other materials. With the arrangement shown in FIG. 1, this is particularly true of the surfaces of the toggle or over-centre clamps 22, some of which are not readily accessible or visible. Other surfaces which are visible can be cleaned, rinsed and even sterilised where necessary, but the clamps themselves can provide a source of potential contamination because some of their surfaces are not readily visible.
In other prior art arrangements, the cover, screen frame, collection hopper and other elements of the sieve can be clamped together using a single band clamp, comprising a V-section hoop which is tightened around the sieve elements to clamp them together. Effective clamping using individual toggle clamps as in FIG. 1 or the known band clamps requires skill and care on the part of the operator, and the procedure is prone to error.
It is therefore an objective of this invention to provide an improved arrangement for securing or clamping the component parts of the separator together.
Embodiments of the invention can also improve the sealing of the various components, i.e. chassis, cover, sieve frames, so that finely divided products do not escape from the product space in the sieve.
In U.S. Pat. No. 5,226,546, there is disclosed a separator construction in which circular sieve frames can be loaded through slots in a side wall of a cylindrical chassis of the separator and then held in position by inflating an annular inflatable tube with the various components of the separator held in position by one or two strap ties which extend parallel to the axis of the chassis and are located on the outside of the chassis and clamp the component parts together at a maximum of two locations. This, we believe, can lead to distortion of the components of the separator, especially of the screen frames, albeit by a very small amount, but to an extent that does allow leakage of material from the separator.